Pseudoephedrine

Pseudoephedrine Hydrochloride is found in over-the-counter cold remedy preparations under trade names including Sudafed. It acts as a blood vessel constrictor, thereby relieving congestion. It is commonly used as a symptomatic treatment for rhinitis, including allergic rhinitis. Unlike antihistamines[?] which interact with allergic reactions, pseudoephedrine only minimizes nasal congestion which may be a consequence of allergy. Pseudoephedrine doesn't cause drowsiness, an undesired effect of many antihistamines. It is also misused as a stimulant.

Pseudoephedrine is chemically similar to methamphetamine although the biological effects are very different. Because of pseudoephedrine's use as a primary reagent in the manufacture of methamphetamine in illicit labs, USA federal law prohibits buying cold preparations containing pseudoephedrine in quantities greater then 3 packages in any 24-hour period.